Question

我正试图在这样的常量上进行左连接：

SELECT 
    [t0].[DeviceId], 
    [t0].[DeviceTypeId], 
    [t0].[UnitId], 
    [t0].[UnitNum], 
    [t0].[ManPhone], 
    [t0].[Status], 
    [t2].[MaintDate] AS [ServiceExpiration]
FROM [dbo].[Devices] AS [t0]
    INNER JOIN [dbo].[CustomerDevices] AS [t1] 
        ON ([t0].[DeviceId]) = [t1].[DeviceId]
    LEFT JOIN [dbo].[Maintenance] AS [t2] 
        ON ([t0].[DeviceId]) = [t2].[DeviceId]
            AND 8 = [t2].ActionId

当我在LINQ中尝试这样的时候，我得到CS1941：

var devices = from d in db.Devices
    join cd in db.CustomerDevices
        on d.DeviceId equals cd.DeviceId
    join serviceExpiration in db.Maintenances
        on 
           new { d.DeviceId, ActionId = 8 } // CS1941
               equals 
           new { serviceExpiration.DeviceId, ActionId = serviceExpiration.ActionId } into j1
    from deviceServiceExpiration in j1.DefaultIfEmpty()

Answer 1

首先尝试维护ActionId == 8，然后使用此加入。

var expirations = from serviceExpiration in db.Maintenances
                  where serviceExpiration.ActionId == 8
                  select serviceExpiration;

var devices = from d in db.Devices
    join cd in db.CustomerDevices
        on d.DeviceId equals cd.DeviceId
    join e in expirations
        on d.DeviceId = e.DeviceId into j1
    from deviceServiceExpiration in j1.DefaultIfEmpty()
    select deviceServiceExpiration;

Answer 2

试试这个

var devices = from d in db.Devices
    join cd in db.CustomerDevices
        on d.DeviceId equals cd.DeviceId
    join serviceExpiration in db.Maintenances
        on d.DeviceId equals serviceExpiration.DeviceId into j1
    from deviceServiceExpiration in j1.Where(c=>c.ActionId ==8).DefaultIfEmpty()

Answer 3

在这里参加晚会，但我遇到了同样的问题，并希望将来帮助任何人。修复是加入子查询。

var devices = from d in db.Devices
    join cd in db.CustomerDevices
        on d.DeviceId equals cd.DeviceId
    join serviceExpiration in (from x in db.Maintenances where x.ActionId == 8 select x)
        on d.DeviceId equals serviceExpiration.DeviceId into j1
    from deviceServiceExpiration in j1.DefaultIfEmpty()

希望这有助于某人。

Answer 4

或在查询中：

var devices = from d in db.Devices
    join cd in db.CustomerDevices
        on d.DeviceId equals cd.DeviceId
    join serviceExpiration in db.Maintenances
        on 
           d.DeviceId
               equals 
           serviceExpiration.DeviceId into j1
    from deviceServiceExpiration in j1.DefaultIfEmpty()
        where serviceExpiration.ActionId  == 8
    select deviceServiceExpiration;

如何在LINQ中加入常量？

4 个答案: